Electromagnetic speaker



Dec. 18, 1934.

JA. JENSEN 1,984,800

ELECTROMAGNET I C SPEAKER Filed April 25, 1929 NVENTOR. /C/C c/S'NSEN BY g E ATTORNEY.

Patented Dec. 1.8, 1934 UNITED STATES PATENT OFFICE l .121.136.111tomi cunifrngl SPEAKER .mk Jongen, oakland, caux. Application Aprile; lsaafserigl No; 357,936

` s claims.y (ol." 417o- 11155) This invention relatesv to loud speakers; and especially relates to .that class commonly called electromagnetic .speakers that are used in connection'with radios.' f i It is one Vof the objects ofthe `present invention to concentrate themagnetic field by providing a gap of varying Vlength betweenthe'pole-pieces.

It is yanother object of :the invention to -pnfo'videL an improved rand-exceptional simple constructed housing, `for vthe cone, that is madeout ofA one piece of sheet metal and is formed in vone pressing operation. l

The invention further consists in the particular combination, 'form of construction 4and association `of the ydifferent elements, suon as described in the following 'specification and possesses other objects and features of advantage, some of which, with'thefforegoing, will be made manifest lin lthe -preferred form Aof the invention which is illustrated in the drawing accompanying and `forming partof the speciilcation.

It is to 'be understood that itl-is not intended to limit .the `invention to the embodiment shown by said drawing land description, as variations maybe adapted within the scope of the inven` tion as set forth in the claims; Y In 'the accompanying drawing: l y 'Figure' 1 is a central longitudinal sectional view of one `type of speaker involving the'in'` vention. s

Figure 2 is a partial sectional and vside -elevaf tional view of one stud usedin the inventions Figure 3 is a perspective View of the coneland sound coil tube support. I f l Figure I4 is a sectional view taken on fline A--A of Figure 1, looking in the Idirection ofthe arrows. Y I A Figure 5 is a perspective'view `of a cut-'out upperpolepiece which may be mounted oni-the central pole to form a gap of lvarying-length.v

Referring in rrdetail to 4the -d-i-ierent- 'parts wherein :like reference characters denote corresponding parts throughout the several views,

numerals 9 and 10 designate two flat pole-pieces s that may be made out of any suitable metal, but are preferably made of standard square cold rolled steel andare held together by a plurality of bolts 12 as illustrated in Figures 1 and 4. The said bolts are made of a size suflicient to properly carry the magnetic flux and are preferably constructed as shown in Figure 2, having a ref` duced threaded portion 12a on` the front end and an internally threaded hole 12b in the rear end.

The front plate 9 is provided with threadedholes into which the said bolts are screwedand are locked thereto by means of lock nuts 15. Therearplatewl is fastened to the bolts by a plurality of ca p screws or bolts 16 that are -projected through the plate 10 and threaded into the tapped 'holes 12b of the bolts 12. A central pole 17 prefer-ably made of soft cold rolled steel',

-is for-med with a reduced portion 17a, and the Atrated'a*certainshape of opening 9e in the front plate 1-9, ibut it is to -be 'denitely understood that anysuitable shapefniay -be used. A shaped upper pole jpiece 20, formed'with spaces 20a preferably as illustrated in Figures 3 and 8, is provided, and is mounted on the front end of the center polepiece 1'7,-and is fastened thereon witha llister f head screw V21 as shown in Fgllre'l. The-upper pole *piece 20 -is-preferably arranged as shown with the spaces 20a, respectively, coincidingwith the spaces in Vthe#opening in the plate 9. The spaces 20a may be provided directly inthe' centrajllpole- 17 if desired. This construction enables the piece A2O to be providedr in different sizes, and also, simplifies machine work.

A cone 22, made out `of paper or ber or any suitable material, such as used lin standard practice, is provided, and is mounted within an respecially constructed cone housing r23' that is fastened on the plate `9 by thestuds 12 and the nuts 1-5 as shown in Figure `1. The cone housing is preferably vmade ,out of one piece of sheet metal and is first b'lankedout .as shown in Figure `6, `after 4whichit is bent into the form as shown irrFigu're 7. The cone 22 is fastened to the housing 23 by means of a circular member 24 that is preferably made out of fiexible material, such as leather, and is glued, or otherwise fastened by any suitable means, to both the housing 23 and the cone 22 as shown in Figure v1. At the small end of the cone, a tube 24, that ispreferably made out of the same material as the cone, is provided and is glued to the cone and extends into the opening 9ek in the front plate 9 and of an inch larger in diameter than the outer diameter of the said member 20 to permit the tube to have longitudinal movement over said member 20 Without having contact therewith, or with the front plate 9.

A thin non-magnetic plate 25, hereinafter called the vibrating plate, that is cut out preferably as shown in Figure 5, is mounted on the ends of the studs 12 and is held tightly against the nuts 15 by the nuts 26. A split metal conc shaped washer 27 as shown in Figure 3 is glued to both the cone 22 and the tube 24, and is fastened to the vibrating plate 25. The said cone washer is provided with a circular end portion 27a that is notched as shown in Figure 3, and the said end portion 27a is mounted in a hole 25a in the vibrating plate and the notched ends thereof are bent firmly around the plate and fastened substantially thereto as shown in Figure 1. A copper coil 28, hereinafter called the sound coil `is mounted around the cone tube 24 and onek end of the sound coil is fastened to the input terminal 275 on the cone washer and the other end of said coil is fastened to the output terminal 27e. Numerals 29 and 30 designate electric conductors that lead from the terminals 27h and 27e to the audio frequency circuit. A copper plate 31 is arranged between the field coil and the sound coill to provide a shield between the two coils to reduce the hum caused by pulsating current. The said copper plate is preferably formed square as shown in Figure 4 and is cut out on the corners to iit closely to the bolts l2 as illustrated.

From the foregoing it will be seen that a magnetic eld will be produced in the air gap 9e when direct current is passed through the field coil 18 and when the sound coil 28 is connected to an audio frequency circuit through electric conductors 29 and 30 it will further be seen that modulated audio currents will pass through the sound coil and will produce a magnetic field of their own that will react upon the strong magnetic eld in the air gap 9e with a `force that is proportional to the current that passes through the sound coil, which will cause said sound coil to vibrate in proportion to the current that passes therethrough, and as said coil is fastened to the cone, the cone will be caused to vibrate in unison with said coil, thus producing sound. It will be noted also that cutting away portions of the pole pieces in no way alters the total magnetic flux but rather concentrates it at the four uncut portions of the gap, therefore the same effective `magnetic ilux is maintained in the gap while, due to the reduction of the length of the gap, the chance of dirt or other foreign matter entering the limited space between the pole pieces and the sound coil is reduced.

A further beneficial result is obtained by this construction, in that eddy currents, with their attendant losses, are reduced due to the fact that there are no closed circuit low resistance paths in either pole piece closely adjacent the sound coil.

Having thus illustrated a certain form of construction and arrangement of parts pertaining to the invention, it is to be understood that the improvements may be embodied in any electromagnetic speaker, which, obviously, may be built up in any suitable manner, the present illustration not being utilized as indicating Ythe only form of construction into which the parts may be made; and it is desired to include in this application for Letters Patent of the United States of America, any and all patentable novelty that exists in the invention disclosed and all that comes within the range of the invention as set forth in the claims hereinafter mentioned.

What is claimed is:

1. A sound reproducer comprising a magnetic circuit, an annular air gap in said circuit, a cylindrical sound coil inserted vin'said air gap, and an actuating means attached to said coil, a portion of said magnetic circuit being removed at said air gap to concentrate the magnetic eld with ,different intensities on different circumferential portions of said cylindrical coil.

2. A sound reproducer comprising av central polepiece, an outer polepiece having an opening surrounding and spaced from the inner polepiece, a circular sound coil positioned within the space between the polepieces, and sound actuating means attached to said sound coil, said polepieces being symmetrically cut away in a plane at right angles to the axis of said coil to cause a concentration of magnetic density on different circumferential portions of said sound coil.

3. A sound reproducer comprising a central polepiece, an outer polepiece having an opening surrounding and spaced from the inner polepiece, a circular sound coil positioned Within the space between the polepieces, and sound actuating means attached to said sound coil, said polepieces being shaped to provide an air gap of varying length in a plane at rightangles to the axis of said coil.

4. A sound reproducer comprising a magnetic circuit having an annular air gap, a sound coil in said gap, and means for causing the flux density intersecting said coil to diier in different circumferential portions of said coil.

5. A sound reproducer comprising a magnetic circuit having an annular air gap, a sound coil in said gap, and means for concentrating the flux in said air gap upon regularly spaced circumferential portions of said coil. s A

6. A sound reproducer comprising a magnetic circuit having an annular air gap, a sound coil in said gap, and means for applying a different iiux density to various portions of said coil around the circumference thereof.

JACK JENSEN. 

